1972 Plymouth Duster Alignment failure

Alright so when i got my duster a little over a year ago, the alighnment was out like crazy, and it could barely be driven down the road (plus eaten through many tires). I recently had a local trusted alighnment shop replace the upper and lower ball joints, tie rods and ends, and made damn sure it would stay alighned.....But as soon as you get 1o0 yards down the road, the alighnment goes wonky and the tires start to squall and the tire starts to eat away on the inside(closest to the edge of the tire ) One of the mechanics mentioned something about the engine in the car having the oil pan hit the idler arm (said the engine and exhaust looks like it came outta a truck). The Mechanics gave me a 6 month warranty, but they were scratching heads trying to figure out what to do next. The car was orriginally a 6 cylinder that has had a 360 dropped in it and the brakes are now disk brakes....Please help guys, I'd love to be able to drive her....and my wallet just got alot lighter without much result